The invention relates to gas filtration. More particularly, the invention relates to filters, such as cigarette filters, methods of making the filters, and methods of using the filters to filter gases, such as mainstream tobacco smoke.
A number of filter materials have been suggested for incorporation into cigarette filters, including cotton, paper, cellulose, and certain synthetic fibers. However, such filter materials generally only remove particulate and condensable components from tobacco smoke, and thus are not optimal for the removal of gas-phase constituents from tobacco smoke.
Cigarettes incorporating filter elements with adsorbent materials have been described, for example, in U.S. Pat. Nos. 2,881,770 to Tovey; 3,353,543 to Sproull et al.; 3,101,723 to Seligman et al.; 4,481,958 to Ranier et al. and 5,568,819 to Gentry et al.; and in European Patent Application No. 532,329.
Different forms of carbon have been described for filtration applications. See, for example, U.S. Pat. Nos. 4,379,465; 4,412,937; 4,700,723; 4,753,717; 4,772,508; 4,820,681; 4,917,835; 4,933,314; 5,059,578; 5,191,905; 5,389,325; 5,510,063; 5,543,096; 5,632,286; 5,685,986; 5,732,718; 5,744,421; 5,820,967; 5,827,355; 5,846,639; 5,914,294; 5,972,253; 6,030,698; 6,090,477; 6,207,264; 6,214,204; 6,257,242 and 6,258,300; and the publications T. D. Burchell et al., xe2x80x9cA Novel Process and Material for the Separation of Carbon Dioxide and Hydrogen Sulfide Gas Mixturesxe2x80x9d, 1997, Carbon, 35:1279-94; T. D. Burchell et al., xe2x80x9cPassive CO2 Removal Using a Carbon Fiber Composite Molecular Sievexe2x80x9d, Energy Conversion and Management, 1996, 37:947-54; and T. D. Burchell et al., Proceedings of 23rd Biennial Conference on Carbon, American Carbon Society, 1997, p. 158.
Sectioned filters have been described, for example, in U.S. Pat. Nos. 3,958,579; 4,774,972; 5,360,023; 5,409,021; 5,435,326; 6,206,007 and 6,257,242.
Despite these developments in filtration, there is a continued need for improved filters and methods for filtering gases.
The invention provides filters suitable for gas filtration. A preferred embodiment of a filter comprises a sorbent including at least two sorbent segments, and a mixing region between two adjacent sorbent segments. The mixing region can be a space and/or it can include at least one mixing segment. The filter can remove at least one selected gas-phase constituent from a gas flow.
In a preferred embodiment, the sorbent includes activated carbon. In another preferred embodiment, the sorbent includes at least one molecular sieve material. In yet another preferred embodiment, the sorbent includes two or more different sorbent materials.
In a preferred embodiment, the sorbent segments include one or more flow channels. Different sorbent segments of the same filter can have the same or a different flow channel configuration to provide tailored filtration and/or fluid flow performance characteristics.
In a preferred embodiment, the filter is a cigarette filter including a mixing region between two adjacent sorbent segments. The filter is capable of removing one or more selected gas-phase constituents from mainstream tobacco smoke.
In another preferred embodiment, a smoking article comprises a filter including a mixing region between two sorbent segments, which is capable of selectively removing one or more selected gas-phase constituents from mainstream smoke.
A preferred embodiment of a method of making a cigarette filter comprises incorporating a filter including sorbent segments and one or more mixing regions into a filter. A preferred embodiment of a method of making a cigarette comprises placing a paper wrapper around a tobacco rod, and attaching such cigarette filter to the tobacco rod to form the cigarette.
A preferred embodiment of a method of smoking a cigarette comprises lighting or heating the cigarette to form smoke and drawing the smoke through the cigarette, where the cigarette comprises a filter including sorbent segments and one or more mixing regions.